1. Field of the Invention
The present invention relates generally to ignition systems for use in internal combustion engines and more particularly to an ignition system for use in internal combustion engines employing magneto-responsive solid state sensing devices.
2. Description of the Prior Art
Ignition of the fuel to air mixture in internal combustion engines by electric spark has been achieved in many ways. Regardless of the system implemented, there exists the fundamental necessity to provide and deliver a high voltage pulse to the spark plugs with sufficient energy content to create an electric arc between center electrodes and ground electrodes of the spark plugs. In addition, the high voltage pulse must be delivered to each spark plug at the appropriate time and for an appropriate duration of time. Modern systems typically have sensor or triggering means that sense, via an angular position of a crankshaft, when a piston in a particular cylinder is entering a power stroke in the engine cycle and relay that information in some manner. Processing circuitry with high voltage, high current switching means is used to energize a primary coil of an ignition coil and a secondary coil delivers a high tension pulse to the spark plugs. One drawback to the known systems is that it is necessary that all the ignition processing circuitry be RF shielded. Poor shielding can lead to system malfunction or complete failure, particularly in those systems that require microprocessors. High tension wires, i.e. spark plug wires, must also be shielded so as not to affect ignition processing circuitry as well as other electronic devices such as car stereos, car phones, and the like.
As stated, sensing and triggering means exist that sense the angular position of an engine's crankshaft either directly or indirectly. Presently, inductive sensing means are most often implemented. Inductive sensing requires that a magnetic field at the sensor change. Although a change in magnetic flux induces a voltage in a conductor, magneto-responsive devices are not always "inductive" in that sense. A magnetic field may be used to effect sensor output in which the magnitude and not a change in flux of the field causes a sensor output to change. Hall effect elements, and the devices in which they are used, are examples of magneto-responsive solid-state devices that do not work on the principle of rate of change induced voltage. Instead, a magnetic field perpendicular to the flow of current causes a difference in electric potential throughout a conductor or semiconductor. The resulting voltage is referred to as the Hall voltage. The output voltage of a sensor of this type as effected by the Hall voltage is independent of the rate of change of the magnetic field being sensed.
The advantages of using a Hall effect device, versus other magnetic means for crank angle sensing, include: (1) smallest package size; (2) low cost; (3) minimum parts count; (4) sharp trigger response; (5) good resistance to environmental effects.
Latching Hall effect devices provide an advantage in that timing intervals can be set with two very small permanent magnets. This contrasts with more involved external means of extending the response of non-latching devices that are known. The prior art teaches the use of a single Hall effect device, namely a bipolar two-output Hall device, that is spaced between a pair of opposing permanent magnets. Dual magnetic flux fields of the same magnitude are generated at the Hall effect device which cancels the effect on the device. A crankshaft mounted disk carries metallic tabs in specific relation to shunt the magnetic field between one and then the other of the magnets and the Hall effect device at predetermined intervals which allows the device to be actuated by the remaining magnetic field at the sensor. One of the outputs of the bipolar Hall device, depending on which field is shunted, relays the sensor output to one of two input channels of a microprocessor. The related output channel of the microprocessor is input to a related coil driver, ignition coil, and then the spark producing means of two of four cylinders. The dwell time, i.e., the time for which a primary coil is energized to saturation before the collapse of the magnetic field in the ignition coil and thereby inducing a high voltage pulse in the secondary coil which is grounded through the spark plugs, is determined by the length of a metallic tab. The longer the tab, the longer the Hall effect device produces a Hall voltage, which, by way of some intermediate circuitry, energizes the primary coil. Similarly, a single magnet and two single output Hall effect devices are taught and function in a like fashion. In both cases, the sensor is arranged to sense the angular position of the crankshaft in direct relation to the crankshaft's rotation. Because the crankshaft makes two complete revolutions per power stroke in a given cylinder in four stroke cycle engines, the ignition coil or coils are fired twice during one complete engine cycle for a particular cylinder. One of the firings is delivered between exhaust and intake strokes and is of no benefit. In fact, this doubles the necessary burden of the system.
Also known in the art is a solid state ignition system utilizing a non-latching Hall effect switch as a means of advancing and retarding the ignition timing. The Hall effect switch is activated by a D.C. biasing voltage which is induced in a coil by permanent magnets carried on the rotatable member of a small, single cylinder, magneto fired engine. The use of the Hall effect switch in this application differs greatly from that previously described.
Examples of the above-described devices may be found in U.S. Pat. Nos.: 4,155,340; 4,508,092; 4,406,272; 5,158,056; 5,014,005; 4,903,674; 3,556,068; 2,768,227; 4,918,569; 5,113,839; 3,587,549; 2,811,672; and 3,621,827. Additionally, French Patent 2,422,044 and U.S. Pat. Nos. 2,675,415 and 2,462,491 may be of interest.